For a project of mine, I'm looking for a simple map editor that would allow me to do the following:

* Custom terrain with hills, mountains, rivers and trees
* Freely placing/rotating buildings
* Ideally freely explore the map, as to create a kind of video

The above in a 3D environment.

Any game that provides such toolset?

You oh should be able to do that in any 3D engine, unity, unreal, godot all spring to mind. Blender also would be great for it and has camera/film options to record video from a 3D scene. That would be my recommendation, and blender is free!

Edit, and if you want proper terrain, then getting a proper terrain editor might be necessary, depends on what you are going for.

Legends of Eisenwald (that takes place in Medieval Europe) has an editor. Though I'm not sure if it's "easy" enough.

Probably WarCraft 3 editor would fit you, but with all Reforged shenanigans you'd have to get the copy of the game from torrents.

I ill have a look at eisenwald.
Is in my library too.

Blender is famous for being over-the-top complexity.
A generic engine will also pose a problem for finding compatible assets.

You mean something like this?
https://store.steampowered.com/app/253370/Axis_Game_Factorys_AGFPRO_v3/

Unity Asset Store has quite a few free assets, including medieval/fantasy themed.

Btw, you can also take a look at Total War: Medieval.

Yes, something like this would be perfect.

Nah, blender has come on leaps and bounds since the old days. It’s now got a normal control system. Also, will not be a problem finding compatible assets as it should be able import almost any type of files.
It’s the best you will find, especially for free. Other tools will be limited.

I just remembered another game/tool which probably would have fit your wantings: Project Spark.

However - as far as I'm aware, that got canned in 2018(?)
You still can buy the XBox disc version, though...but I have no clue, as to how useful the program still is nowadays, with all the proper infrastructure missing.

https://www.amazon.de/Microsoft-4TS-00019-Project-Spark-Xbox/dp/B00KX1LY56

This may sound silly but Minecraft is the tool you're looking for if you're just looking for a medieval map editor. There even are bulding related mods that have the same features you're looking for, such as rotating buildings you've made.

In no other "editor" I've been able to produce landscapes with the freedom such as Minecraft. If you have the time you can create entire worlds in Minecraft. In fact, theres like a whole industry within the online part of minecraft where artists build worlds for online servers. Some of the stuff I've seen is pretty nuts and you shouldn't underestimate Minecraft as a extremly potent tool to create words.

I've created whole worlds in Minecraft from a flat plane and so did hundreds of thousand of other folks. It only takes time, but its time well spent. You may also learn something about geology and architecture, because creating believeable medieval words and landscapes (also Castles, Villages or Cities) take tons of practise as well.

Or just mod Skyrim. The Creation Kit is powerful enough to create their own worlds, even if you're not a game dev and just starting out. There are some mods for it that don't have anything to do with Skyrim itself.

Or wait for Mount and Blade 2: Bannerlord to comes out (Early Access should be next month). If you knew about modding in Mount and Blade: Warband, you will be able to produce medieval landscapes and buildings fairly easily.

The problem with modern medieval games is that using dev tools like Unity to create believeable worlds is that they take a lot of skill and practice (years in fact). Simply because you have to make everything from scratch.

There are some good suggestions made by others in this thread, however, most editors you can find online are pretty restricted in what they're able to do or work only for a certain type of game. Or require quite some programming knowledge or are quite time consuming to figure out. If you just want to spend around half a year creating something majestic, Minecraft is definitely the way to go.

I'd recommend the Leveleditor of Neverwinter Nights 2.
It has everything you're asking for and is relatively easy to use.

I'll also echo Unity (just take some time to learn to move around in it and use keyboard shortcuts like Q, W, E, R, T, for placing and transforming things), but first check out Unity's asset store to see if you find things you like. (I imagine you'll find quite a bit though since it's a hugely popular engine.)

Thanks for the wealthy replays.

I'm not building a world nor a videogame, so I was looking for something really basic, but I think I've got a number of interesting options.